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Biomedical subjects

R G Murray

Publications and source records attributed to R G Murray.

At least 145 records · Page 8Linked to original sources
PubMed1975

Relation between extent of coronary artery disease and severity of hyperlipoproteinaemia.

Lipoprotein analyses were performed in 133 male patients and were correlated with the coronary arteriographic findings. The prevalence of hyperlipoproteinaemia was significantly higher in those patients with coronary artery disease (P less than 0-02). In addition, the more extensive the degree of coronary artery pathology the higher were the plasma concentrations of total cholesterol, triglyceride, and low density lipoprotein (LDL) cholesterol. Hyperlipoproteinaemia was more prevalent in the younger patients with coronary artery disease (P less than 0-02).

Age Factors↗
PubMed1975

Ultrastructural effects of lysozymes on the cell wall of Caryophanon latum.

When Caryophanon latum was exposed to egg white lysozyme in isotonic sucrose and observed by phase-contrast microscopy, protoplasts emerged along the length of the trichomes, apparently at sites corresponding to cross septa. Electron microscopy of sections revealed that this enzyme initially attacked the core of the septal peptidoglycan and delamination of septa resulted. The inner densely staining layer of the lateral and polar wall (considered to contain peptidoglycan as the major component) remained intact except for destruction at the advancing tip of partial septa; protoplasts or cell debris could escape from the gaps formed at developing septa. Treatment of intact trichomes with pronase, a lipase - phospholipase C mixture, EDTA, glutaraldehyde, or heat, before exposure to egg white lysozyme did not alter this pattern nor did it render the remaining peptidoglycan more susceptible to attack. The wall material external to the peptidoglycan was solubilized by pronase. The peptidoglycan remaining after lysozyme treatment was not morphologically changed by treatment with pronase. Lysozyme derived from Chalaropsis hydrolyzed incomplete septa initially, while the lateral and polar wall and complete septa were degraded later. Therefore, it is most probable that the inner dense layer does contain the peptidoglycan component and that some biochemical maturation distinguishes the substrate for these enzymes in the lateral wall and septa.

Bacteria↗
PubMed1974

Septum formation in Escherichia coli: characterization of septal structure and the effects of antibiotics on cell division.

Septa can be demonstrated in sections of Escherichia coli strains B and B/r after fixation with acrolein and glutaraldehyde. The septum consists of an ingrowth of the cytoplasmic membrane and the mucopeptide layer; the outer membrane is excluded from the septum until the cells begin to separate. Mesosomes have also been observed. The septum is highly labile and, except in the chain-forming strains, E. coli D22 env A and CRT 97, not easily preserved by standard procedures. The labile nature of the septum may be due to the presence of autolysin(s) located at the presumptive division site. Blocking division by addition of ampicillin (2 to 5 mug/ml) to cells of E. coli B/r produces a bulge at the middle of the cells; bulge formation is stopped by addition of chloramphenicol. Cephalosporins also induce bulge formation but may stop cell elongation as well as division. Bulge formation, due to the presumed action of an autolysin(s), may be an initial step in the septation sequence when the mucopeptide is modified to allow construction of the septum. In a nonseptate filament-forming strain, PAT 84, which ceases to divide at 42 C, bulge formation only occurs in the presence of ampicillin at the time of a shift-down at 30 C or at 42 C in the presence of NaCl (0.25 to 0.34 M). Experiments with chloramphenicol suggest that the filaments are fully compartmentalized but fail to divide owing to the inactivation, rather than loss of synthesis, of an autolysin at 42 C.

Acrolein↗
PubMed1974

Superficial macromolecular arrays on the cell wall of Spirillum putridiconchylium.

Electron microscopy of the cell envelope of Spirillum putridiconchylium, using negatively stained, thin-sectioned, and replicated freeze-etched preparations, showed two superficial wall layers forming a complex macromolecular pattern on the external surface. The outer structured layer was a linear array of particles overlying an inner tetragonal array of larger subunits. They were associated in a very regular fashion, and the complex was bonded to the outer, pitted surface of the lipopolysaccharide tripartite layer of the cell wall. The relationship of the components of the two structured layers was resolved with the aid of optical diffraction, combined with image filtering and reconstruction and linear and rotary integration techniques. The outer structural layer consisted of spherical 1.5-nm units set in double lines determined by the size and arrangement of 6- by 3-nm inner structural layer subunits, which bore one outer structural layer unit on each outer corner. The total effect of this arrangement was a double-ridged linear structure that was evident in surface replicas and negatively stained fragments of the whole wall. The packing of these units was not square but skewed by 2 degrees off the perpendicular so that the "unit array" described by optical diffraction and linear integration appeared to be a deformed tetragon. The verity of the model was checked by using a photographically reduced image to produce an optical diffraction pattern for comparison with that of the actual layers. The correspondence was nearly perfect.

Cell Wall↗
PubMed1974

Electron microscope study of septum formation in Escherichia coli strains B and B-r during synchronous growth.

The formation of cell wall septa was monitored in Escherichia coli B and B/r during synchronous growth in glucose media at 37 C by means of electron microscopy. The visible events of septation comprised the following sequence, starting at about 30 min of incubation: (a) bleb formation of the outer membrane; (b) invagination of mucopeptide and cytoplasmic membrane (with associated mesosomes); the outer membrane is excluded from the septum; (c) formation of a cross-wall; (d) ingrowth of the outer membrane during cell separation. The septum is composed of a fold of cytoplasmic membrane plus mucopeptide, and the latter is a double structure, composed of two opposed lamellae separated by an electron-transparent gap. Experiments with chloramphenicol and nalidixic acid suggested that division could occur in the presence of these inhibitors once a round of deoxyribonucleic acid replication is completed. The initial stages of septation, as estimated by the potential of the cells to produce bulges in the presence of ampicillin, may involve the modification of mucopeptide by hydrolases at the end of the C period. Assembly of the septum may occur during the first half of the D period by means of precursors synthesized during the preceding C period.

Ampicillin↗
PubMed1969

Fractionation and characterization of the plasma and mesosome membrane of Listeria monocytogenes.

Protoplasts of Listeria monocytogenes strain 42 were fractionated after control lysis on a Ficoll (a polysucrose) density gradient. Visually, five zones could be recognized in the gradient. The first one was composed of amorphous cytoplasmic solutes (fraction 1a) and a mixture of particles (fraction 1b). These were: (i) light particles that were lipase-sensitive and composed of six subunits and (ii) heavy particles, sensitive to ribonuclease and devoid of fine structure. The second zone consisted of tubules and vesicles still harboring cytoplasmic components (fraction 2), whereas the third zone contained only empty vesicles and protoplast ghosts (fraction 3). The material congregating into the fourth zone was morphologically identical to that of the third (fraction 3a). The fifth and heaviest zone contained a mixture of (i) particles without any substructure and (ii) partly lysed protoplasts (fraction 4). Fractions 1b and 4 were the richest in nucleic acids (ribonucleic acid, 11.4 and 9.4%, respectively; deoxyribonucleic acid, 5.1 and 4.8%, respectively), whereas fraction 1b had the highest protein contents (74.6%). Phospholipids were mainly found in fractions 2 and 3. Except for fraction 1, all materials contained significant amounts of protein-bound phosphorus. The main concentrations of four enzymes were: glucose-6-phosphate dehydrogenase (fraction 1a); adenosine triphosphatase and reduced nicotinamide adenine diphosphate oxidase (fraction 3); nitro blue tetrazolium chloride reductase (fraction 2). Fractionation of strain 42 after addition of (32)P during the mid-log phase of growth revealed that the radio-activity was mainly detected in fraction 1b, when growth in the presence of the marker was allowed for 10 min, and in fraction 2, when growth was allowed for 90 min. The vesicles of fraction 2, often tubular, are probably of mesosomal origin, whereas those of fraction 3, which are always spherical, represent, most likely, the bulk of the cell plasma membrane. Our data showed slight chemical differences between these two fractions, but the differences in enzymatic activities and lipid-phosphorus incorporation during long pulse experiments were most dramatic.

Adenosine Triphosphatases↗